System for identifying the location of a device within a patient&#39;s body in order to locate the fossa ovalis for trans-septal procedures

ABSTRACT

A system and method for identifying the location of a medical device within a patient&#39;s body may be used to localize the fossa ovalis for trans-septal procedures. The systems and methods measure light reflected by tissues encountered by an optical array. An optical array detects characteristic wavelengths of tissues that are different distances from the optical array. The reflectance of different wavelengths of light at different distances from an optical array may be used to identify the types of tissue encountered, including oxygenated blood in the left atrium as detected from the right atrium through the fossa ovalis.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of patent application Ser. No.12/696,488, filed Jan. 29, 2010, entitled OPTICAL METHOD OF IDENTIFYINGTHE LOCATION OF A MEDICAL DEVICE WITHIN A PATIENT'S BODY IN ORDER TOLOCATE THE FOSSA OVALIS FOR TRANS-SEPTAL PROCEDURES, the entirety ofwhich is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to a system and method for opticallyidentifying the position of a medical device within a patient, andparticularly for using optical methods for identifying an optimal regionof the interatrial septum of the heart for puncturing during atrans-septal procedure.

BACKGROUND OF THE INVENTION

Catheterization procedures have become the preferred methods fortreating a variety of heart conditions. A catheter has a long, flexiblebody that may be introduced into the vasculature and guided into theheart or another organ of the body. By incorporating various medicaldevices, for example an ablation device, into the distal portion of acatheter, it may be used for ablation, as well as other proceduresincluding angioplasty, dilation, biopsy and other procedures within thehuman heart and elsewhere.

For certain cardiovascular procedures, a catheter is inserted into anartery or vein in the leg, neck, torso or arm and threaded through thevasculature into the heart. FIG. 1 (prior art) shows a human heart 10into which a catheter 12 has been introduced. In a common procedure, acatheter 12 enters into the right atrium 14 through the inferior venacava 16. From the right atrium 14, the catheter may be directed to otherregions of the heart.

Many procedures require introducing the catheter to the left atrium 18.One method of entering the left atrium 18, known as a trans-septalprocedure, includes first entering the right atrium 14 through the venacava 16 and then puncturing the interatrial septum 20. The interatrialseptum 20 is the portion of the atrial wall which divides the left andright atria. Once the interatrial septum 20 is punctured, the end of thecatheter 12 proceeds into the left atrium 18 where it may performablation or other medical treatments.

At the center of the interatrial septum 20 is a thin fibrous regionknown as the fossa ovalis 22. The fossa ovalis 22 is surrounded by themuscular tissue 24 of the atrial walls. The fossa ovalis 22 isrelatively thin and does not include muscular tissue, making it thegenerally preferred region in which to puncture the interatrial septumduring trans-septal procedures. Puncturing of the muscular tissuesurrounding the fossa ovalis causes unwanted damage to the heart.

Accurate localization and identification of the fossa ovalis presentssignificant challenges. The fossa ovalis is invisible to current imagingtechniques used to visualize a catheter during intercardial procedures,such as fluoroscopy. As a result, a physician must rely upon his ownskill to position the tip of a catheter prior to puncturing the fossaovalis.

Another difficulty encountered during trans-septal procedures is thevariance in the thickness of the fossa ovalis between differentindividuals. Without knowing the approximate thickness of the fossaovalis being punctured, a surgeon does not know how far a puncturingdevice on a catheter must travel or how much force is required in orderto traverse the fossa ovalis. Thus an additional risk inherent intrans-septal procedures is that too much force will be applied to thecatheter, resulting in piercing both the fossa ovalis and otherstructures within the heart such as the heart wall or aorta inunnecessary and undesirable locations.

One method of identifying the fossa ovalis uses spectroscopy and theability of light to penetrate some thickness of tissue. The blood in theright atrium, where the catheter is introduced into the heart, is filledwith deoxygenated blood that has a characteristic absorption spectrum 30shown in FIG. 2. The absorption spectrum 30 of deoxygenated, rightatrium blood differs significantly from the absorption spectrum 32 ofthe oxygenated blood found in the left atrium, particularly within therange of 600 nm to 805 nm. Because the fossa ovalis is very thin, theoxygenated blood of the left atrium may be viewed by an optical deviceabutting the fossa ovalis.

The fossa ovalis is the only region of the right atrium where oxygenatedblood and its characteristic spectrum may be observed. Thus, a cathetermay incorporate an optical device that illuminates the blood and tissuesurrounding the catheter tip and detect the spectrum reflected back.When such an optical device detects the absorption spectrum ofoxygenated blood, the device is abutting the fossa ovalis. Thus, bymoving a catheter tip about the right atrium and particularly around theatrial wall of the right atrium, an operator of a catheter device mayidentify the fossa ovalis prior to puncturing the interatrial septum.

However, the nature of the optical device may create difficulties inaccurately identifying the fossa ovalis. The light being reflected andobserved by the detector must travel far enough to be reflected by theoxygenated blood of the left atrium. Where an optical device has anemitter for illuminating surrounding tissue and a detector for observingthe absorption spectra positioned very close to each other, most of theobserved reflected light is reflected from the fossa ovalis itself andnot the oxygenated blood of the left atrium. Thus, the fossa ovalis maynot be accurately localized.

If, on the other hand, the emitter and detector are relatively farapart, the detector may observe light reflected from the left atriumeven though it traveled through the muscular wall, not the fossa ovalis.As a result, a portion of the interatrial septum having muscular tissuemay be mistakenly identified as the fossa ovalis. Thus, a trans-septalpuncture may be inadvertently made through muscular tissue, causingunnecessary damage.

It is therefore desirable to provide a system and method for identifyingthe location of a medical device within a patient and particularly foraccurately identifying when a medical device is abutting the fossaovalis. It is also desirable to be able to measure light reflected fromdifferent distances from the tip of the catheter within the body.

SUMMARY OF THE INVENTION

The present invention provides a method for identifying the location ofa medical device within a patient. Light is emitted from an emittertoward at least one tissue within a body. The reflected light ismeasured by two or more receivers which are separated by differentdistances from the emitter. The measured reflected light may then beused to calculate a remittance value for two wavelengths at each of thereceivers. A remittance ratio is then calculated by dividing theremittance values of the two wavelengths for each receiver. This may bedone with wavelengths ranging between 600 nm and 1000 nm. Specificwavelengths 660 nm and 940 nm may be measured using this technique.

In addition, the slope of the remittance values over the wavelengthrange may be calculated for the light detected by each of the receivers.Optionally, the curvature over the range of wavelengths may becalculated to identify the characteristic spectra of oxygenated bloodand other tissue. The emitter and receivers may be incorporated onto aface plate.

A medical device for identifying the location of a medical device withina patient's body includes an intravascular catheter and an opticalarray. The optical array has one or more emitters for emitting light andreceivers for detecting reflected light, wherein the receivers are notall equidistant from the emitter. The medical device also includes aspectrometer in communication with the emitter and the receivers. Theemitter and receivers may be on a face plate. The optical array may beinserted into a lumen in a catheter and protrude from a distal region ofthe catheter and have two face plates.

A face plate may be annular and surrounding an opening to a lumen in thecatheter. The face plate may abut an interatrial septum and may be movedacross the interatrial septum and detect light from a plurality oflocations along the interatrial septum.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a view of a human heart having a catheter inserted into theright atrium;

FIG. 2 is a graph of absorption spectra of various tissues found withinthe human heart;

FIG. 3 is an embodiment of a medical device constructed in accordancewith the principles of the present invention;

FIG. 4 is an enlarged view of the optical array of the medical device ofFIG. 3;

FIG. 5 is an alternative embodiment of a medical device constructed inaccordance with the principles of the present invention;

FIG. 6 is an alternative embodiment of an optical array constructed inaccordance with the principles of the present invention;

FIG. 7 is an alternative embodiment of an optical array constructed inaccordance with the principles of the present invention;

FIG. 8 is an alternative embodiment of an optical array constructed inaccordance with the principles of the present invention;

FIG. 9 is a perspective view of the medical device of FIG. 3 in a humanheart;

FIG. 10 a graph of absorption spectra of various tissues found withinthe human heart;

FIG. 11 is an enlarged view of the optical array of FIG. 4 abutting aninteratrial septum;

FIG. 12 is an enlarged view of the optical array of FIG. 4 abutting thefossa ovalis of an interatrial septum;

FIG. 13 is an enlarged view of the optical array of FIG. 4 abuttinganother interatrial septum; and

FIG. 14 is an enlarged view of the optical array of FIG. 5 abutting afossa ovalis.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a system and methods of use thereof forcharacterizing the optical characteristics of tissue surrounding amedical device within a patient. In particular, the present inventionprovides a medical system and methods of use thereof for identificationof a targeted tissue type.

Referring now to the drawing figures in which like referencedesignations refer to like elements, an embodiment of a medical system40 constructed in accordance with principles of the present invention isshown in FIG. 3. The medical system 40 generally includes a catheter 42having an optical array 44 coupled to a spectrometer 46 through anumbilical system 48.

The catheter 42 comprises a proximal portion 50, a distal portion 52 andan elongate flexible tubular body 54. The distal portion 52 of thecatheter 42 may include an ablation element, a balloon and/or one ormore sensors to monitor various parameters including for examplepressure, temperature, flow rate, volume, or the like. The catheter 42may also optionally include one or more lumens disposed within theelongate body, thereby providing mechanical, electrical, and/or fluidcommunication between the proximal portion 50 and the distal portion 52of the catheter. The catheter 42 may be made of a flexible material andmay be typically 80 cm to 100 cm long, but may optionally be shorter orlonger. The body 54 of the catheter 42 may be typical of catheters foruse in trans-septal procedures that include introducing the distalportion of the catheter into the right atrium of the heart andproceeding into the left atrium by puncturing the interatrial septum.All or a portion of the catheter 42 may optionally be comprised ofradiopaque material or may include one or more radiopaque markers.

The umbilical 48 may be a bundle of optical fibers or electrical wiresplacing the spectrometer 46 in communication with the optical array 44.Other umbilicals may optionally be used to operate other sensors orother devices, for example an ablation device. The spectrometer 46 mayinclude processors that may analyze optical data, for example thewavelengths and amplitudes of the emitted light and the wavelengths andamplitudes of detected reflected light at particular wavelengths. Thespectrometer 46 may provide one or more graphs of the data or mayoptionally perform mathematical analyses on the data, as explained inmore detail below.

Referring now to FIG. 4, the optical array 44 is shown in more detail.The optical array 44 includes an emitter 56 for emitting light directedat tissue surrounding and in front of the distal portion 52 of thecatheter 42 of FIG. 3. The emitter 56 may be composed of any devicesuitable for emitting light, for example a light-emitting-diode orsimilar device. Optionally, the emitter 56 may be a plate or window,comprised of for example glass, acrylic or other transparent material,in communication with an optical fiber that provides light to theemitter 56. The emitter 56 also may simply be the end of an opticalfiber. The light emitted by the emitter 56 may be a broad band of lightranging over several wavelengths or may be of selected discretewavelengths. The emitter 56 may further include a filter (not shown) forfiltering the type of light emitted. Optionally, a plurality of emittersmay be used.

The optical array 44 also includes two receivers 58 and 60 for detectinglight reflected from adjacent tissue(s). As used herein, the term“tissue” refers generally to any tissue within the human body, such asmuscle, fibrous tissue, blood, and others. The receivers 58 and 60 maybe comprised of any device known to detect light. The receivers may be aplate or window, comprised of for example glass, acrylic, or othertransparent material, in communication with an optical fiber andtransmitting detected light to the optical fiber. The receivers 58 and60 may also simply be the end of an optical fiber. The receivers 58 and60 may optionally be devices that measure various parameters of detectedlight, for example wavelengths, amplitudes and/or other parameters, andgenerate an electrical or other signal containing information about themeasured parameters. The receivers 58 and 60 may detect a broad range ofwavelengths or only selected wavelengths, and may optionally includefilters for selecting which wavelengths are detected.

The optical array 44 may be located on the face plate 62 positioned atthe distal portion 52 of the catheter 42. The face plate 62 may besubstantially planar and optionally may be substantially perpendicularto the longitudinal axis of the catheter 42. Optionally, the distalportion 52 of the catheter 42 may include a radiopaque marker, notshown, which may be on the face plate 62. Optionally, all or part of thecatheter 42 may be composed of a radiopaque material.

FIG. 4 also illustrates the relationship between the distance betweenthe emitter 56 and the receivers 58 and 60 and their respective targetdepths of penetration 64 and 66. As used herein, the term “target depth”refers generally to the penetration distance of light from emitters towithin tissue where the main spatial distribution of light reaches amaximum depth. There is a linear correlation between the distancebetween an emitter and a receiver and a distance light travels into atissue in order to be detected. The optical array 44 therefore mayacquire spectral information from tissue(s) at different distances fromthe optical array because it has two receivers that are at differentdistances from the emitter. The distance 68 separates the emitter 56 andthe receiver 58 from each other. As a result, any light detected by thereceiver 58 travels to the depth of penetration 64 or further. Lightreflected from a point closer to the optical array 44 may not bedetected by receiver 58.

Similarly, reflected light detected by the receiver 60 travels at leastto the target depth of penetration 66. Because the distance 70 separatesthe emitter 56 and the receiver 60 from one another, any light detectedby receiver 60 travels at least to the target depth of penetration 66.Where the distance 70 is twice the distance 68, the depth of penetration66 for the receiver 60 will be approximately twice the distance 64 forthe receiver 58. Incorporation of the emitter 56 and the receivers 58and 60 into the face plate 62 may allow these distances to remainconstant.

While the correlation between the distance between an emitter and areceiver and the depth of penetration may be generally linear, theactual depth of penetration for a given distance between an emitter andreceiver may be affected by a variety of factors and may be determinedempirically. The correlation may depend on the wavelengths used, thegeometry of the emitter and the receiver, the type of tissue, and otherfactors.

Referring now to FIG. 5, an alternative medical device 80 has an opticalarray 82 including an emitter 84 and a series of four receivers 86, 88,90 and 92 linearly arranged at increasing distances from the emitter 84.The optical array 82 may be insertable into the lumen of a catheter suchthat it may be removably placed at the distal portion of the catheterinstead of as an integral component of the catheter itself. The opticalarray 82 may also include a face plate 94 into which the emitter 84 andthe receivers 86, 88, 90 and 92 may be incorporated. An umbilical 96connects the optical array 82 to a spectrometer 98 that may providelight to be emitted to the emitter 84 and may measure light detected bythe receivers 86, 88, 90 and 92 in order to analyze the spectroscopicdata collected. Optionally, the umbilical 96 may include electricalwires capable of transmitting signals from the emitter 84 and thereceivers 86, 88, 90 and 92 to the spectrometer 98. Because all fourreceivers 86, 88, 90 and 92 are different distances from the emitter 84,they all observe light traveling to different depths of penetration.

Referring now to FIG. 6, a catheter 100 has an optical array 102 and alumen 104 that extends its length and allows various instruments to beinserted into the catheter 100 such that they protrude from the lumenopening 106. For example, a piercing or puncturing instrument such as aneedle may be passed through the lumen 104 and out of the opening 106 tofacilitate puncturing of the fossa ovalis once it has been localizedusing the optical array 102. The puncturing instrument may then bewithdrawn and replaced with an ablation or other instrument.

The optical array 102 of the catheter 100 may be located on an annular,planar face plate 108 surrounding the lumen opening 106. The face plate108 may be flat and lie in a plane substantially perpendicular to thelongitudinal axis of the catheter 100. The emitter 110 emits light ofdiscrete wavelengths or a band of wavelengths. The receivers 112 and 114may be equidistant from the emitter 110. The two receivers 112 and 114may have the same depths of penetration. The receiver 116 may befarthest from the emitter 110 and allows the optical array 102 to gatherspectroscopic data from regions farther from the face plate 108.

Referring now to FIG. 7, an optical array 120 having two face plates 122and 124 may be collapsed and inserted into a lumen 126 in a catheter128. Once it has traversed the length of the catheter 128 and protrudesout at the distal portion 130 of the catheter 128, the optical array 120may be expanded. The optical array 120 may be mounted on a wire 132which supports the optical array 120 and may have a radiopaque marker104 to assist in observing the position of the optical array 120. Theface plates 122 and 124 may be supported by the cables 134 and 136respectively. The optical array 120 may be expanded so that the faceplates 122 and 124 may be parallel and the emitter 138 and the receivers140 all align in a single plane. By adjusting the cables 134 and 136,the face plates 122 and 124 may be adjusted such that they may not beparallel and/or not lie in the same plane.

Referring now to FIG. 8, an optical array 150 may be collapsed so thatit may fit through the lumen 152 of the catheter 154. Upon exiting thelumen 152, the optical array 150 may be expanded using cables, notshown. The optical array 150 may be mounted on a wire 156 which may havea radiopaque marker 158 and a receiver 160. The expanding arm 162 alsomay have a radiopaque marker 164 and an emitter 166. Optionally, some orall of the optical array 150 may be comprised of a radiopaque material.The expanding arm 162 expands to a distance from the wire 156 determinedby the length of the cable 168. Similarly, the expanding arm 170 expandsto a distance from the wire 156 determined by the length of the cable172, and includes a radiopaque marker 174 and a receiver 176. Theexpanding arm 178 includes a radiopaque marker 180 and a receiver 182and expands to a predetermined distance determined by the length of thecable 184. The expanding arms 162, 170 and 178 each have a specificlength such that when expanded, the emitter 166 and the receivers 160,176 and 182 all lie in the same plane. By adjusting the lengths of thecables 138, 142 and 184, the plane in which the receivers lie may bewarped so that it may be concave or convex. Additional expanding armsmay optionally be included to provide additional receivers. The opticalarray 150 does not include a face plate. By using expanding arms thatwhen expanded place the emitter 166 and receivers 160, 176 and 182 atknown positions relative to each other, their respective depths ofpenetration may be determined.

Referring now to FIGS. 9-13, in an exemplary method of use, the medicalsystem 40 of FIG. 3 may be used to acquire optical information for atargeted tissue area. Specifically, the medical system 40 may be used tolocalize the fossa ovalis during a trans-septal procedure. Catheter 42may be introduced into the right atrium 190 after being routed throughthe vascular system, for example, through the inferior vena cava 192.The superior vena cava may optionally be utilized for jugular orsubclavian insertions. Traversing the vasculature and positioning of theoptical array 44 may be aided by imaging techniques (fluoroscopy, etc.).Once in the vicinity of the targeted tissue, the optical array 44 may beadvanced at least partially into contact with the atrial wall, of whichthe interatrial septum 194 is a portion. The interatrial septum 194,comprised of the fossa ovalis 196 and muscular tissue 198, separates theright atrium 190 and the left atrium 200. Once the optical array 44 atthe distal region of the catheter 42 is in the right atrium 190, thecatheter may be guided such that the optical array 44 abuts theinteratrial wall. The distal portion of the catheter moves about theinteratrial wall of the right atrium 190 as the optical array 44 emitslight and detects the absorption spectra of the tissue(s) it encounters.When an absorption spectrum consistent with the fossa ovalis 196, suchas the spectrum 197 in FIG. 10, the catheter 42 may remain in thatlocation while the fossa ovalis 196 is punctured.

FIG. 10 shows the spectra observed by the optical array 44 when itencounters different tissues within the heart. The spectrum 191characteristic of deoxygenated blood may be observed by the opticalarray 44 while traveling through the vena cava and into the rightatrium. The spectrum 201 is the absorption spectra of the oxygenatedblood of the left atrium. The spectrum 197 may be observed when theoptical array 44 abuts the fossa ovalis and is an attenuated version ofthe oxygenated blood spectrum 201. The fossa ovalis spectrum 197 has thenegative curvature and increased remittance between 600 nm and 805 nmfound in the spectrum 201, but the remittance may be lowered across thelength of the spectrum, resulting from travel through the fossa ovalis196. Actual spectra observed at a fossa ovalis may be more or lessattenuated than spectrum 197 shown here, but may generally retain thecurvature and slope of oxygenated blood. Muscular tissue may generallyhave a spectrum similar to spectrum 199, reflecting a substantial amountof light directed at it.

Referring now to FIG. 11, the optical array 44 abuts against a location202 on the interatrial septum 194. The location 202 includes both themuscular tissue 198 and the fibrous fossa ovalis 196. The depth ofpenetration 64 may be located within the muscular tissue 198 and thespectra detected by the receiver 58 may be indicative of musculartissue, similar to the spectrum 199 in FIG. 10. The depth of penetration66, however, may be located in the left atrium 200 and therefore thespectrum detected by the receiver 60 may be similar to an attenuatedleft atrium blood spectra similar to the spectrum 197 in FIG. 10,indicating the fossa ovalis. The absorption spectrum detected by thereceiver 60 may be weak as most of the light may be unable to penetratethe muscular tissue 198. The receivers do not both detect a spectrumindicating the fossa ovalis, indicating that the optical array 44 likelydoes not completely abut the fossa ovalis 196. The optical array 44 maythen be repositioned in a new location in order to determine whether alocation exists at which both receivers detect spectra similar to thespectrum 197 indicative of the fossa ovalis.

Referring now to FIG. 12, the optical array 44 abuts against a location204 on the fossa ovalis 196. As a result, both depths of penetration 64and 66 are within the left atrium 200 and therefore both receivers 58and 60 detect spectra having the characteristics of oxygenated bloodsimilar to the spectra 197 and 201 in FIG. 10, indicative of the fossaovalis 196. By moving the optical array 44 across the atrial wall asshown in FIGS. 11 and 12, the fossa ovalis 196 may be accuratelylocalized. The change in spectra observed by the receivers is notinstantaneous, but rather the spectra change slowly as the optical arrayis moved across the interatrial septum. The optical array 44 maytherefore be moved about the interatrial septum until a spectrum isobserved by all of the receivers that has the most similarity to thespectrum 201 of oxygenated blood, and may appear similar to theattenuated fossa ovalis spectrum 197.

FIG. 13 shows the optical array 44 in contact with a relatively thickfossa ovalis 206. The thicknesses of fossa ovali vary significantlybetween individuals. When an optical array 44 encounters a thick fossaovalis 206, the light reflected from the depth of penetration 64 may notbe within the left atrium 208. As a result, the spectrum of lightdetected by the receiver 58 may be relatively flat and similar to thespectrum 199 in FIG. 10, inconsistent with the fossa ovalis. Were thereceiver 58 the only receiver, then the fossa ovalis 180 may not belocalized. However, the receiver 60 has a greater depth of penetration66, allowing it to detect the blood of the left atrium 208. As a result,the receiver 60 detects a spectrum similar to that of the spectrum 197in FIG. 10, indicating the fossa ovalis. The optical array 44, byincluding two or more receivers, allows an operator to determine thepresence of the fossa ovalis 206 despite its relative thickness.

As an example, the measurements of the spectra may be similar orcomparable to a weighted average between spectra 199 and 201, withweighting biased more towards spectra 201 for receiver 60, and the netspectra approaching that of 197 as the ratio of spacing over thicknessincreases. Due to the non-discrete nature and range of potentialthicknesses of the fossa ovalis (or other targeted tissue), a clinicallyestablished threshold may be used to differentiate.

Referring now to FIG. 14, the optical array 82 of medical device 80 inFIG. 5 has four receivers, each a different distance from the emitter84. The receiver 86 has a depth of penetration 210. The receiver 88 hasa depth of penetration 212. The receiver 90 has a depth of penetration214. The receiver 92 has a depth of penetration 216. This arrangement ofreceivers allows a determination of the thickness of the fossa ovalis218. The receivers 86 and 88 have depths of penetration 210 and 212 thatmay be less than the thickness of the fossa ovalis 218 in this exampleand will thus detect spectra similar to the spectrum 199 of FIG. 10. Thereceivers 90 and 92, on the other hand, have depths of penetration 214and 216 that may be greater than the thickness of the fossa ovalis 218and may detect spectra more similar to the spectrum 197 of FIG. 10. Fromthis, an operator may determine that the thickness of the fossa ovalis218 may be greater than the depth of penetration 212 but less than thedepth of penetration 214. Knowledge of the thickness of the fossa ovalis218 may be beneficial in allowing an operator to estimate the amount offorce that must be applied to a puncturing instrument. By applying acorrect amount of force to the puncturing instrument, the possibility ofusing too much force and damaging tissue within the left atrium isminimized.

Because the actual spectra observed may not be as clearly distinct asthe spectra 191, 197 and 199 shown in FIG. 10, various algorithms may beused to estimate that actual thickness of the fossa ovalis. That is, thespectra observed by receiver 88 and receiver 90 may have more subtledifferences than the clear differences between spectra 197 and 199.Empirically obtained data may be used to compare to actual data obtainedusing the optical array in order to accurately determine the thicknessof a fossa ovalis. One such example of determining the desired locationmay include estimating the thickness of the fossa ovalis wall based on aprojection from 1 or more measurements in conjunction with clinicallymeasured empirical data. For example, the equation Sm=(1−f)×Sfo+f×Slamay be used to approximate the location and spectra characteristics,where “Sm” is the measured spectra, “Sfo” is an empirically determinedcharacteristic spectrum of the fossa ovalis when the separation distanceis less than half the fossa ovalis thickness, and “Sla” is the spectrumcharacteristic of the left atrium when the probe is in pure left atriumblood or the separation distance is several times greater than the fossaovalis thickness. “f” is a scaling factor in the range of 0 to 1. Given“Sm” and predetermined clinical “Sfo” and “Sla” (for each separationdistance), we may solve for “f,” which may be empirically correlated towall thickness for a given probe design and separation distance. Aseries of “f” values (denoted “fi”) corresponding to multiple separationdistances can improve the confidence in the thickness estimate overbroader ranges.

Due to potentially widely varying offset shifts in the spectraamplitude, this exemplary approach may require normalizing the spectraby a discrete wavelength such as the isosbestic point, such that “Sm,”“Sfo,” “Sla” are each normalized by their respective values atwavelength of approximately 805 nm.

Multiple methods of analysis exist by which spectra detected may becharacterized. For example, an optical array may detect reflected lightat two wavelengths, one between 600 and 805 nm and one between 805 and1000 nm. Specifically, the optical array may detect light at wavelengthsof 660 nm and 940 nm. Remittance for each wavelength is calculated bydividing the amplitude of light reflected by the amplitude of lightemitted at each wavelength. As can be seen in FIG. 10, deoxygenatedblood absorbs more light between 600 nm and 805 nm, illustrated by thespectrum 30, while oxygenated blood reflects more light in this band,illustrated by spectra 32 and 34.

Oxygenated and deoxygenated blood share an isobestic point at 805 nm. Atwavelengths above the isobestic point oxygenated and deoxygenated bloodhave similar but opposite spectral responses compared with the responsesthe within 600 to 805 nm range. Thus, by comparing the remittance valuesdetected at 660 nm and 940, for example by dividing the remittance at660 nm by the remittance at 940 nm to generate a remittance ratio, thepercentage of oxygen saturation of blood may be accurately determined. Ahigh remittance ratio indicates oxygenated blood as detected. Such areading may indicate that an optical array is proximate to the fossaovalis.

The above described technique of normalizing reflectance at onecharacteristic wavelength using reflectance at an isobestic or constantwavelength may be used to identify regions within the body based uponblood oxygenation, but may also be used to identify any region ortissue(s) by characteristic wavelengths.

Other methods may be used to identify the characteristic spectra ofdifferent tissue(s) including blood. For example, the entire spectrabetween 600 nm and 1000 nm can be detected using the optical array anddisplayed on a screen for an operator to view. Alternatively, discretewavelengths can be measured using either a broad band emission oremission only of the light to be detected.

For example, light at wavelengths between 700 and 800 nm may bedetected. In this region, oxygenated left atrial blood exhibits asubstantially constant negative slope, as shown in the spectra 197 and201 in FIG. 10. The muscle of the interatrial septum exhibits a flatspectrum in this region while deoxygenated, right atrial blood exhibitsa zig-zag spectrum, dipping markedly at 760 nm. Thus, the fossa ovalismay be localized by identifying the region of the interatrial septum inthe right atrium where an optical array reads a spectrum having arelatively constant, negative slope between 700 and 800 nm. The regionof the atrial wall having the most negative slope in this wavelengthrange may be the fossa ovalis.

There are several known mathematical methods suitable for accuratelyidentifying these different spectra. For another example, the spectra197 and 201 in FIG. 10 are concave down in the range of 600 nm to 760nm. Thus, these spectra have a negative second derivative, or curvature.As used herein, the term curvature refers to the second derivative of aline and is a measure of the rate at which the slope of a line changesover a range. The spectrum 191 has a relatively steady positive slope inthis region, resulting in a curvature close to 0. A spectrometerconnected to the optical array could first measure the remittance atthree or more points in this range, calculate the slopes betweenadjacent points, and calculate the curvature. The fossa ovalis may belocalized by identifying the region of the interatrial septum having themost negative curvature.

A spectrometer may perform some or all of these calculations onreflected light detected by a receiver to identify the region of theseptum at which the most left atrial, oxygenated blood is detected. Thisregion may generally be the fossa ovalis. Any of these above techniquesmay be used to identify different tissues of within the right atrium sothat the fossa ovalis may be identified. Once the fossa ovalis is found,a piercing apparatus may be introduced so that one or more medicaldevices may enter the left atrium.

The optical arrays described above may be used to identify andcharacterize tissue(s) other than the anatomical localization of thefossa ovalis. For example, other tissues, both normal and thosepossessing inherent physiological and pathological conditions ofinterest, having characteristic spectra may be identified using theabove methods and systems described. Identification and characterizationof particular tissues adjacent to a medical device aid in a variety ofmedical procedures.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A system for assessing a cardiac septum toidentify the location of a fossa ovalis, the system, comprising: anintravascular catheter including a distal portion, a proximal portion,and a lumen therebetween, the intravascular catheter further comprisingan optical array comprising a light emitter configured to emit lighttoward the septum, a plurality of receivers configured to detectreflected light from the septum, and an annular face plate surroundingan opening to the lumen, wherein at least two of the plurality ofreceivers are each positioned on the face plate at different distancesfrom the emitter; and a spectrometer in communication with the emitterand the plurality of receivers, the spectrometer including one or moreprocessors programmed to analyze optical data received from theplurality of receivers, the one or more processors further programmed todetermine: the optical array is at a location that abuts the cardiacseptum when a first receiver of the plurality of receivers detects afirst spectrum and a second receiver of the plurality of receiversdetects a second spectrum; the optical array is at a location proximatecardiac wall tissue other than the cardiac septum when the firstreceiver and the second receiver of the plurality of receivers eachdetects the first spectrum; and the optical array is at a location thatabuts the fossa ovalis when the first receiver and the second receiverof the plurality of receivers each detect the second spectrum.
 2. Themedical system of claim 1, wherein the catheter has a longitudinal axisand the annular face plate lies in a plane that is substantiallyorthogonal to the longitudinal axis of the catheter.
 3. The medicalsystem of claim 2, wherein the emitter and plurality of receivers arepositioned radially around the lumen on the face plate.
 4. The medicalsystem of claim 3, wherein the plurality of receivers comprises at leasta first receiver, a second receiver, and a third receiver.
 5. Themedical system of claim 4, wherein the first receiver and the secondreceiver are located approximately 180° from each other on the annularface plate, and the emitter and the third receiver are locatedapproximately 180° from each other, the first and second receivers eachbeing located approximately 90° from the emitter and third receiver. 6.The medical system of claim 1, wherein the plurality of receiverscomprises two receivers.
 7. The medical system of claim 1, furthercomprising a radiopaque marker coupled to the optical array.
 8. Themedical system of claim 1, wherein the emitter and plurality ofreceivers all lie on the same plane.
 9. The system of claim 1, whereinthe one or more processors are programmed to determine the depth of thefossa ovalis based at least in part on the optical data received fromone or more of the plurality of receivers.
 10. The system of claim 1,wherein the one or more processors are programmed to assess thesuitability of the fossa ovalis for a medical procedure.
 11. A systemfor assessing a cardiac septum to identify the location of a fossaovalis, the system comprising: an intravascular catheter including: adistal portion, a proximal portion, and a lumen therebetween; an annularface plate surrounding an opening to the lumen at a distal region of thecatheter; an optical array radially arranged on the face plate, theoptical array having a light emitter configured to emit light toward thefossa ovalis, a first receiver, a second receiver, and a third receiver,the first, second, and third receivers configured to detect reflectedlight from the fossa ovalis, the first receiver and the second receiverbeing located approximately 180° from each other on the annular faceplate, the emitter and the third receiver being located approximately180° from each other, and the first and second receivers each beinglocated approximately 90° from the emitter and the third receiver; and aspectrometer in communication with the emitter and the first, second,and third receivers, the spectrometer including one or more processorsprogrammed to determine: the optical array is at a location that abutsthe cardiac septum when at least one of the first and second receiversdetects a first spectrum and the third receiver detects a secondspectrum; the optical array is at a location proximate cardiac walltissue other than the cardiac septum when the third receiver and atleast one of the first and second receivers each detects the firstspectrum; and the optical array is at a location that abuts the fossaovalis when the third receiver and at least one of the first and secondreceivers each detect the second spectrum.